Devices for imaging body cavities or passages in vivo are known in the art and include endoscopes and autonomous encapsulated cameras. Endoscopes are flexible or rigid tubes that pass into the body through an orifice or surgical opening, typically into the esophagus via the mouth or into the colon via the rectum. An image is formed at the distal end using a lens and transmitted to the proximal end, outside the body, either by a lens-relay system or by a coherent fiber-optic bundle. A conceptually similar instrument might record an image electronically at the distal end, for example using a CCD or CMOS array, and transfer the image data as an electrical signal to the proximal end through a cable. Endoscopes allow a physician control over the field of view and are well-accepted diagnostic tools. However, they do have a number of limitations, present risks to the patient, and are invasive and uncomfortable for the patient. Their cost restricts their application as routine health-screening tools.
An alternative in vivo image sensor that addresses many of these problems is capsule endoscope. A camera is housed in a swallowable capsule along with a radio transmitter for transmitting data to a base-station receiver or transceiver. A data recorder outside the body may also be used to receive and record the transmitted data. The data primarily comprises images recorded by the digital camera. The capsule may also include a radio receiver for receiving instructions or other data from a base-station transmitter. Instead of radio-frequency transmission, lower-frequency electromagnetic signals may be used. Power may be supplied inductively from an external inductor to an internal inductor within the capsule or from a battery within the capsule.
In an autonomous capsule system, multiple images along with other data are collected during the course when the capsule camera travels through the gastrointestinal (GI) tract. The images and data after being acquired and processed are usually displayed on a display device for a diagnostician or medical professional to examine. However, each image only provides a limited view of a small section of the GI tract. It is desirable to form (stitch) a single composite image or a small number of composite images with a larger field of view from multiple capsule images. A large image can take advantage of the high-resolution large-screen display device to allow a user to visualize more information at the same time. An image stitching process may involve removing redundant overlapped areas between images so that a larger area of the inner GI tract surface can be viewed at the same time in a single composite image. A larger image can provide a broader view of a significant portion of the inner GI tract surface.
However, in typical capsule images from the GI tract, there are a lot of non-GI objects such as bubbles and debris that will affect image registration, which is a crucial step in image stitching to transform multiple images into one common coordinate system. Subsequently, these non-GI objects will affect the quality of image stitching. Therefore, it is desirable to develop a method that may identify such non-GI objects and takes it into consideration in image registration to improve the accuracy.